Soybean is a vegetable of high nutritive value and contains fat and protein in a substantial proportion and therefore, the vegetable has a very wide range of applications.
Although it has been relatively easy to separately extract individual constituent ingredients of soybean from the vegetable, and means for extracting soybean oil or producing soybean with fat removed from the raw soybeans have been widely known, it has been heretofore considered relatively difficult to obtain processed soybean goods retaining all the soybean constituent ingredients therein as they are and especially, soybean powder from the raw soybeans. The reason for the difficulty is that it has been difficult to devise effective means for removing the odor inherent in raw soybeans from the vegetable (the odor emitted from soybean fat). Especially, when raw soybeans are processed to deodorize at high temperatures on the one hand, the soybeans are rendered to a fat removed state resulting in decomposition of the nutrients of the vegetable. When raw soybeans are processed at low temperatures on the other hand, because oil pressing is performed when the raw soybeans are pressed flat, the nutritive value of the soybeans is reduced, and moreover, the soybeans are not perfectly deodorized.
As indicated by the foregoing, the conventional methods for producing soybean powder have deprived the raw soybeans of a substantial portion of the constituent ingredients of the vegetable, and especially the fatty ingredients of the vegetable to the degree that the processed soybeans have to be subsequently provided with new fatty ingredients. Thus, the conventional methods have been uneconomical and the particle size of soybean powder obtainable by the conventional methods has been limited to the range of 200-300 mesh to the utmost.
Furthermore, the conventional methods for producing soybean powder have the disadvantages that when means are provided to increase the proportion of residual fatty ingredients in the obtained soybean powder, the deodorization degree of the soybean powder is not only reduced, but the particles of the powder are necessarily made coarse because the residual fatty ingredients have a high viscosity.